1. Field of the Invention
This invention relates to hydrocarbon gas sensors and more particularly to such gas sensors designed to monitor the presence of hydrocarbon gas and in particular hydrocarbon gas leakage from the valve stem of a valve in a gas flow line such as found in petrochemical and petroleum refineries and the like.
2. Background of the Invention
There is need as a matter of storage efficiency and environmental protection for valving as used in petroleum and petrochemical lines and the like to have incorporated therewith sensing mechanism by which leakage of gas from the valving can be monitored on a continuing basis so that gas leakage is promptly detectable when it occurs and can be corrected.
Sensors and sensor materials responsive to the presence of even minute amounts of hydrocarbon gases are known such as disclosed in Dolan U.S. Pat. Nos. 3,045,198, 4,224,595 and 4,237,721, for example. Such gas sensors in general are comprised of electrically conductive adsorbent particles embedded in a resilient supporting substrate and are typically in cylindrical form such as shown in FIG. 4 of U.S. Pat. No. 3,045,198. Typically, in such sensors, the substrate is comprised of a resilient material such as rubber or silicone and the electroconductive particles are selected from the group consisting of platinum, platinum black, aluminum, silver, gold, tantalum, carbon, or any other well-known electrically conductive particles and can comprise particles of various sizes and mixtures of such particles. However, as presently known, such gas sensors are difficult and inefficient to use to detect hydrocarbon gas leakage in the vicinity of the stem of a petrochemical or like valve because a conventional sensor, in present form at least, even when placed next to a valve stem, is adjacent to only a small portion of the valve stem surface and exposed to only a small portion of the escaping gas if such gas is present.